C++ program to develop a text based calculator where you can do addition, subtraction, multiplication and division

Question

So the issue i'm having is that when I run the program, it asks for the first input but after i give the operator, the output screen just stops and i have to force quit the output screen. I am using while loops to have the user input as many numbers as they want and when they enter = symbol it should end the program and print the output.

//  C++ program to develop a simple text based calculator where you can do addition, subtraction, multiplication and division.
#include <iostream>
using namespace std;
class calci
{
        private:
            char op; // variable for the operator
            double no;   // variable for getting input numbers    
            double out; // for the output
        
        public:
            void input(char ,double,double);    //to accept input values as well as calculate the output
            
            void output();      //to print the output
};
void calci :: input(char op,double no,double out)
{   op= '+';        //given as a default value for op so that the while loop can start
    
    while(op != '=')    // Used just to make the user input as many numbers as they want untill they give a '=' sign
    {
        std::cout <<"Enter the first number:"<<endl;
        std::cin >>no;
        std::cout <<"\nEnter the operation to be performed with this number";
        std::cout <<"\nEnter + for Additon \nEnter - for Subtraction \nEnter * for multiplication \nEnter / for division \nEnter = to produce the output"<<endl;
        std::cin >>op;
        while(op != '=')
        {
            switch(op)
            {
                case '+' :
                    out=out+no;
                    break;
                case '-' :
                    out=out-no;
                    break;
                case '*':
                    out=out*no;
                    break;
                case '/':
                    out=out/no;
                    break;
                default:
                    break;
            }
        }
    }
    
}
void calci :: output()
{ 
    cout<<"the final answer is"<<out;
    
}
int main() 
{   
    calci c;
    std::cout << "Hello!"<<endl;
    c.input('+',2.0,2.0);
    c.output();
    return 0;
    
}

Answer 1

i have fixed the program, removing class. I have used just one function.

//A C++ program to develop a simple calculator where you can do addition, subtraction, multiplication and division with as many numbers as you want.


#include <iostream>
using namespace std;

int main()
{
    char op;    //variable to accept operators
    double no,n1;   //variables to accept input numbers
    double out;     //variable to calculate the output
    cout<<"Hello!"<<endl;
    cout<<"Enter the first number: ";
    cin>>n1;
    out=n1;
    while(op != '=')
    {   std::cout << "\nEnter the operation to be performed ";
        std::cout << "\nEnter \"+\" for Additon \nEnter \"-\" for Subtraction \nEnter \"*\" for multiplication \nEnter \"/\" for division \nEnter \"=\"  to end calculation"<< endl;
        cin>>op;
        if(op == '=')
            goto printing;
        else
        {
            std::cout << "Enter the next number:" << endl;
            std::cin >> no;
            switch(op)
                {
                    case '+' :
                        out = out + no;
                        break;
                    case '-' :
                        out = out - no;
                        break;
                    case '*':
                        out = out * no;
                        break;
                    case '/':
                        out = out / no;
                        break;
                    default:
                        break;
                }
          }
    }
    printing:
      cout<<"The final answer is ="<<out;
    return 0;
}

Answer 2

the while do loop is an endless loop. The breaks inside the switch-case statement end the switch-case. They dont effect the while loop. One possiblity to solve the problem is to move the 'std::cin >>op;' in the inner loop.

void calci::input(char op, double no)
{   
    out = 0.0;
    std::cout << "Enter the first number:" << endl;
    std::cin >> no;
    std::cout << "\nEnter the operation to be performed with this number";
    std::cout << "\nEnter + for Additon \nEnter - for Subtraction \nEnter * for multiplication \nEnter / for division \nEnter = to produce the output"<< endl;
    
    while(op != '=')
    {
        std::cin >>op;
        switch(op)
        {
            case '+' :
                out=out+no;
                break;
            case '-' :
                out=out-no;
                break;
            case '*':
                out=out*no;
                break;
            case '/':
                out=out/no;
                break;
            default:
                break;               
        }
    }
}

There are many more problems

1. The calculation does not output the correct result. Because you use the out parameter in the input function. Take a look to the scope of a variable
2. the out variable in calci is not initialized. Your program has undefined behaivour
3. the op parameter of input does not effect the calculation, since the first line override the parameter
4. the outer while loop does not effect the caluculation.